Quick-change barrel



gwve/wfom gill]: 11 ww y W cl'n're'nt'e E- c. E. SIMPSON QUICK CHANGE BARREL.

Filed April 4, 1950 II/II/I/IM/III/I/I/I/I/I/ Jan. 20, 1953 Patented Jan. 26, 1953 UNITED STATES QUICK- CHANGE BARREL Clarence E. Simpson, Wilbraham, Mass, assignor to the United States of America as represented by the Secretary of War Application April 4, 1950, Serial No. 153,954

2 Claims. (01. 42-75) (Granted under Title 35, U. S. Code (1952) sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to firearm barrels and more particularly to improved means for effecting rapid replacement of barrels in automatic firearms.

A serious drawback in the operation of fully automatic firearms is the tendency of the barrel to overheat during long continuous bursts of fire and thereby detract from its maximum endurance life and accuracy. Such drawback is customarily overcome by replacing the overheated barrel with a cold, unused one Whenever the opportunity presents itself in order to maintain the operational efficiency of the firearm. Consequently, various devices have been provided for the purpose of avoiding any direct contact with the hot metal of the barrel during removal thereof from the firearm. However, these prior art devices have almost invariably required the use of additional parts such as handles or other protective coverings which, of course, tend to increase the overall weight of the firearm as well as complicate the barrel disassembly procedure.

It is therefore an object of the present invention to provide in an automatic firearm simple and reliable means for rigidly securing a quick change barrel therein.

It is a particular object of this invention to provide in an automatic firearm a barrel adapted for rapid disassembly and replacement without the use of tools or the necessity for manual handling of the barrel itself.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. 1 is a fragmentary longitudinal sectional view showing the barrel of this invention locked to the firearm and showing in dotted outline the path of movement of the rear end of the barrel upon disassembly from the firearm:

Fig. 2 is a fragmentary sectional view showing the details of the front barrel bearing and showing in dotted outline the path of movement of the front end of the barrel upon disassembly from the firearm;

Fig. 3 is a transverse cross-sectional view taken along the line 33 of Fig. 1;

Fig. 4 is a sectional view similar to Fig. 2 but showing the details of the front barrel bearing used in a gas operated firearm; and

Fig. 5 is a fragmentary view of Fig. 1 but showing the additional construction required when the quick change barrel is used with a gas op erated firearm.

There is shown in Fig. l a firearm receiver 5 arranged to suitably house a reciprocating bolt 6 having a firing pin 1. Fixedly secured within receiver 5 by suitable means (not shown) is a barrel extension 8, here shown as cylindrical in form but not necessarily limited to such configuration. Extension 8 is provided with a longitudinal bore 9 therethrough adapted to slidably receive the front end portion of bolt 6. A substantially rectangular cutaway portion In is provided at the front end of barrel extension 8 and extends upwardly from the bottom thereof to form a semi-circular arch portion concentric with bore 9. A semi-circular locking rib l2 concentric with arch portion projects downwardly therefrom for a purpose to be disclosed. At the junction of arch portion and the remainder of barrel extension 8 there is also provided a semicircular clearance recess l l having its vertical axis arranged to form a small angle relative to the vertical axis of extension 8. As a result, a portion of the vertical wall surface l3 formed by rectangular cutaway portion H3 slopes rearwardly and upwardly as shown at l6 from a point slightly below the horizontal centerline of barrel extension bore 9.

A barrel II is of a conventional design but is provided with an annular groove I 5 adjacent the breech end thereof and of sufficient width and depth to matingly engage with rib l2 when completely assembled to extension 8 as best illustrated in Fig. 1. Moreover, the longitudinal distance between the rear surface of rib l2 and the vertical portion l3 of the wall surface formed in barrel extension '8 by cutaway portion I0 is equal to the longitudinal distance between the rear end of barrel H and the vertical rear wall formed by annular groove [5. Thus, when barrel II is fully assembled to barrel extension 8, the rear surface of rib I2 and vertical wall surface I3 serve to rigidly hold barrel II against longitudinal movement relative to extension 8. At the same time, inclined wall portion l 6 introduces a limited clearance space between barrel II and extension 8 for permitting a swinging downward movement of the breech end of barrel H for unlocking from extension 8 as will be hereinafter explained. Such clearance space, however, does not detract from the proper closure of the breech in the battery position of the gun.

A spring-biased pin l1 extends transversely through receiver 5 and is arranged to releasably support barrel II in its locked position. Barrel II is thus securely locked to extension 8 against any tendency for longitudinal shifting movement during the discharge of a cartridge therefrom. Yet, as will be hereinafter shown; barrel II is free to fall of its own weight out of extension 8 when the support of pin I1 is withdrawn.

In the particular firearm here disclosed, re-

ceiver 5 extends forwardly to form a barrel jacket 3. As best indicated at I9 and in Figs. 1 and 3, jacket I8 is open at the top and bottom thereof along substantially its entire length. Opening 20 thus provides access for the assembly and disassembly of barrel I. The front end of jacket I8 is provided with a fixed annular front barrel bearing 2| having an axial opening 22 therethrough for slidably receiving the muzzle end of barrel H. An upper peripheral wall surface 23 of opening 22 is tapered forwardly and upwardly as shown at 24 in Figs 2 and 4 for a distance slightly greater than half the width of bearing 2| so as to form a larger elliptical circumference at the forward end of opening 22 than the diameter thereof. The lower peripheral wall surface 25 of opening 22 is similarly tapered as shown at 26 but in a direction opposite that of taper 24. Hence, barrel II can be tilted an appreciable amount from the horizontal in order to permit slidable rearward movement of the muzzle end thereof through opening 22 while the breech end is out of its horizontal locked position. Yet when barrel II is locked to extension 8 as previously explained, the horizontal peripheral wall portions 23 and 25 of opening 22 are of sufiicient length to adequately support the weight of barrel I.

In view of the foregoing, it can readily be seen that it is an extremely simple matter to replace a barrel in the firearm whenever so desired. To remove barrel II from the firearm, it is merely necessary to retract pin 1 out of suppor ing engagement with barrel H whereu on the breech end thereof will fall out of 4 extension cutaway portion I0 simply through its own weight. Due to the clearance between the inclined wall portion [6 of extension 8 and the rear end of barrel II, the breech portion thereof is free to break its rigid locked connection with extension 8 and fulcrum about the peripheral edge formed by the junction of tapered wall surface 26 and horizontal portion 25 of opening 22. Thus barrel II will swing downwardly through open portion 20 of barrel jacket I8 as indicated by the dotted outline shown in Fig. 1 until the inclination of the rear end is suificient to cause the muzzle end to slide rearwardlv out of front barrel bearing 2|. of barrel II is halted by the ground, it is merely necessary to thrust the entire weapon suificiently forwardly to completely disengage the muzzle end of barrel H from bearing opening 22. Then a new or different barrel can be assembled to the firearm merely by inserting the muzzle end into front barrel bearing 2| and moving the breech end upwardly into locking engagement with barrel extension 8 while the retaining pin I1 is held retracted. Release of such pin will automatically complete locking of barrel II in,

the firearm.

While the firearm disclosed in Fig. 1 is of the recoil type, the barrel locking means of this invention is equally applicable to a gas operated If this swinging movement I firearm. As illustrated in Fig. 4, a conventional gas cylinder 21 is suitably provided adjacent the front end of barrel jacket I8. A gas port 28 in barrel H is aligned with a gas port 29 in gas cylinder 21 through a passage 30 formed through the upper portion of bearing 2|. In order to assure correct alignment of gas port 28 with passage 30 when barrel is in its locked position, there is provided in barrel extension 8 a fixed stud 3| arranged to extend into a suitable .hole 32 in the breech end of barrel Therefore, barrel I must be positioned so that stud 3| will engage in hole 32 thereby properly qualifying gas port 28 with gas passage 30. Otherwise, assembly and disassembly is identical to the procedure previously explained.

Accordingly, the construction herein presented assures extremely rapid and simple replacement of barrels in automatic firearms without requiring any manual contact with the hot barrel during the step of disassembly.

I claim:

1. In a gas operated automatic firearm having a tubular receiver extending substantially the entire length of the firearm and a gas cylinder fixedly secured to the front end of the receiver, the gas cylinder being provided with a gas port, the combination of, a front barrel bearing fixedly secured adjacent the front end of the receiver, a barrel slidably carried by said bearing and having a gas port therein, gas passage means in said bearing interconnecting said barrel gas port with the gas cylinder gas port, a tubular barrel extension fixedly secured in the receiver and having a bore extending longitudinally therethrough, said extension having a substantially rectangular cutaway portion at the front end thereof extending upwardly therein and terminating in a contiguous arcuate upper end arranged to form an arch portion concentric with said extension bore, a semi-circular locking rib projecting downwardly from said arch portion and concentric therewith, a fixed stud disposed rearwardly of said locking rib and projecting downwardly into said cutaway portion, said barrel having an annular groove adjacent its breech end and a vertical recess disposed rearwardly of said groove, said vertical recess being in longitudinal alignment with said barrel gas port and parallel thereto, said breech end of said barrel being constructed and arranged to enter into said extension cutaway portion and mate with said arch portion whereby said locking rib engages in said annular groove to lock said barrel against longitudinal movement, said fixed stud simultaneously enga ing in said vertical recess of said barrel to position said gas port thereof in alignment with said interconnecting gas passage in said barrel bearing, a releasable pin transversely mounted in the receiver for supporting the breech end of said barrel in engagement with said locking rib in said barrel extension, fulcrum means in said barrel bearing constructed and arranged to permit a downward swinging movement of said barrel thereabout, and clearance means between said extension and the rear end face of said barrel for permitting said swinging movement of said barrel solely under the influence of gravity when said pin is withdrawn from supporting engagement with the underside of said barrel.

2. In a recoil operated firearm having a receiver, a barrel extension fixedly mounted in the receiver and having a cutaway portion in the forward end thereof opening upwardly from the underside to terminate in an arch-like portion forming a vertical end wall surface, said cutaway portion including a relief portion originating at a point on said vertical wall surface below the central longitudinal axis thereof and sloping upwardly and rearwardly at a slight angle to the vertical to extend into the'underside of said arch-like portion, said barrel extension having an arcuate locking rib concentric with said archlike portion and depending therefrom to project into said cutaway portion forwardly of and parallel to said vertical end wall surface. a barrel having an annular groove adjacent the rear end thereof and arranged to fully receive said locking rib when said barrel is assembled into said barrel extension cutaway portion with the rear end surface of the former in intimate contact with said vertical end wall surface of the latter, fulcrum means in the front end of the receiver for supporting the muzzle end of said barrel, and a release pin transversely mounted in said receiver forwardly of said barrel extension and against the underside of said barrel for holding said barrel in engagement with said extension whereby the rear Wall surface of said rib and said end wall surface formed by said cutaway portion 00- operate to prevent reciprocal movement of said barrel relative to said extension, said relief portion being arranged to permit unassisted pivotal movement of said barrel about said fulcrum 6 means when said release pin is rendered inoperative.

CLARENCE E. SIMPSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 534,691 Hepburn Feb. 26, 1895 2,163,144 Holek June 20, 1939 2,455,608 Rosengren Dec. 7, 1948 FOREIGN PATENTS Number Country Date 383,754 Great Britain Nov. 24, 1932 

